1. Field of the Invention
The invention relates to apparatus for flow of a liquid medium, for example a heat exchanger, having a plurality of parallel vertical pipes the bottom and top ends of which open into a bottom chamber and a top chamber respectively, for supply and discharge respectively of the medium, mass of particles fluidisable by the flowing medium being present.
2. Description of the Prior Art
Apparatus of the type described above is illustrated for example in U.K. patent Specification No. 1,592,232. Such apparatus can be very effectively used for performing physical and/or chemical processes and is especially useful as a heat exchanger. The medium flowing through the pipes is in this case one of the heat exchanging media, e.g. water, and the pipes are surrounded by the other medium.
The known apparatus is operated so that the granular mass (or mass of particles) in the pipes and the top and bottom chambers is fluidised without the mass being carried as a whole in the direction of the flow of the medium. An operating state is also sought in which the particle movement in each of the parallel pipes is virtually identical, so that the particles are not carried from the one pipe into another pipe. This stationary operating state results in appreciably better heat transfer and therefore to a greater capacity of the apparatus as a heat exchanger. The light scouring effect of the particles on the pipe walls also has a cleaning effect, whereby the risk of dirtying e.g. with boiler scale, is greatly reduced.
A limitation of the known apparatus is that the speed of flow of the medium may not be so great that the particles are carried off through the medium discharge. As a consequence of the improved heat transfer rate achieved by the presence of the particle mass, a lower flow speed of the medium means that, under certain circumstances, the desired heat transfer can be achieved in shorter pipes, but in order to obtain a sufficiently high flow capacity the number of parallel pipes must be large. This may lead to large diameters of the pipe plates which hold the pipes and much costly drilling work in order to prepare these pipe plates.